In, Ga, and Se were coevaporated to form precursor films of (In[sub [ital x]],Ga[sub 1[minus][ital x]])[sub 2]Se[sub 3]. The precursors were then converted to CuIn[sub [ital x]]Ga[sub 1[minus][ital x]]Se[sub 2] by exposure to a flux of Cu and Se. The final films were smooth, with tightly packed grains, and had a graded Ga content as a function of film depth. Photovoltaic devices made from these films showed good tolerance in device efficiency to variations in film composition. A device made from these films resulted in the highest total-area efficiency measured for any non-single-crystal, thin-film solar cell, at 15.9%.

Using a manufacturing friendly process we have developed effective techniques for incorporating Ga in CIGS films. In one techniques we configure the Ga to form an effective BSF and to reduce point defects in the SC region while not increasing the band gap. This results in collection lengths of 2 {mu}m and J{sub {infinity}}{close_quote}s which are consistently in the 40mA/cm{sup 2} range. In a second technique we alloy Ga in the SC region and increase the band gap. This results in mild deterioration of both bulk and surface properties attributable to an unoptimized incorporation environment. The surface properties are shownmore » to be dominated by recombination lifetime which varies systematically with the Se flux environment during surface formation. These insights are providing the foundation for ongoing advances in device performance and imply no fundamental limitations to performance for these processing techniques. {copyright} {ital 1997 American Institute of Physics.}« less

Highlights: ► Wide band gap CAGS thin films have been obtained by selenization of evaporated metallic precursors. ► Direct nonlinear dependence of the band gap energy with the Al/(Al + Ga) ratio is found. ► The bowing parameter decreases when the CAGS film thickness increases. ► The Cu at% remains constant in depth, together with some Al, Ga and Se gradients. ► Surface is strongly oxidized but the oxidation is relatively low in bulk. - Abstract: Wide-band gap chalcopyrite semiconductors have a great interest due to their potential application in multi-junction thin film solar cells or as window layers. Polycrystallinemore » CuAl{sub x}Ga{sub 1−x}Se{sub 2} (CAGS) thin films have been prepared by selenization of evaporated metallic precursor layers on bare and Mo-coated soda lime glass substrates. The optical properties of CAGS films of 2 thicknesses have been analyzed by spectrophotometry in the visible-infrared (VIS-IR) and the compositional characteristics have been studied by energy dispersive analysis of X-rays (EDAX) and X-ray photoelectron spectroscopy (XPS). The optical transmission increases and the band gap energy shifts toward higher values as the Al content increases, which indicates the partial substitution of Ga by Al. The dependence of the band gap with the composition has resulted to be nonlinear and a bowing parameter of b = 0.62 and b = 0.54 for 0.6 μm and 1.1 μm-CAGS samples, respectively, has been obtained. XPS data have shown an Al, Ga and Se composition gradient in depth and a surface strongly oxidized. However, XPS reveals that the Cu composition remains constant in depth and the oxidation is relatively low in bulk increasing slightly in the interface with Mo/SLG. Moreover, samples with high Al content reveal a higher contribution of CuO in depth.« less